When I try to livestream anything, my preview box and the video on my channel is just a black screen, my cursor is the only thing that shows up and the audio is fine. I was able to livestream right after I turned my computer on from updates and when I tried to do it again it was doing the same thing with the black screen. My sister was able to livestream on this same computer but on a different user account a few weeks ago.

My computer is a Gateway SX2801 (Pentium(R) Dual-Core CPU), with 6 GB of RAM. I don't have any cameras connected to my computer, I'm just trying to livestream myself drawing on art programs.
Here's the speedtest results:

I've been able to stream on this computer many many times before with no problems. I got it rebooted back to factory settings a few weeks ago, could this have anything to do with it?

I also tried restarting my channel, the problem is still happening.

EDIT: When I made the resolution smaller, I was able to see what I was streaming and so did everyone else, but as I tried to make it bigger it appeared black again. I tried messing with the video settings on the Preferences but it's doing the same thing.

Your speed test was run to Irvine CA, could you run it again to New York NY? What is your breaking point for resolution; at which point does the stream turn black? Upload bandwidth could contribute to this, as you'd need to have good speeds to New York in order to support high resolutions and/or high bandwidth.

So you need good internet speed to make resolutions bigger, huh? Well, that explains my problem then, my internet has been very terrible lately so now we know why my streams have been going black.

I was able to stream a larger resolution today, but it says my CPU usage is 80% or more, even on the smallest resolution with few programs running, but that's fine as long I get to stream now (on days when my internet is working).